Graphing Calculator - Interactive graph analyzer

This add-in implements an interactive graph creator and
analyzer. It lets one visually examine how various cells affect an Excel
formula. Since it uses the contents of one or more Excel cells, the
program is not limited to plotting graphs with known equations but the content
of anything that can be put in an Excel cell!

Figure 1

The values in the cells that affect the plotted cells can be changed through
the controls on the userform, which, of course, is customized to the graph
currently being analyzed.

Installation

Start by downloading the
zip version.
Unzip the add-in file to a directory of your
choice.

In Excel, use Tools | Add-Ins...
to load the add-in. Depending on where you
installed the file in the above step, you may have to
click the Browse... button
and locate the file.

Make sure that your security setting allows
the loading of the add-in. For versions of Excel
after 2000, the easiest way to load the add-in is to
ensure your security is set (temporarily, if you
otherwise prefer another setting) to Medium. When
Excel warns you about opening a file containing macros,
you must select the 'Enable Macros' option.

The top part of the user form defines what is analyzed. Based on what
is specified, the lower portion of the user form will have custom controls for
the current graph. If the five fields in the top part of the user form are
locked, click the Change button. This
will unlock them and convert the Change button into the Update button.

Figure 2

Note that the software uses a different type of technique than most of us
might be familiar with to select worksheet cells. This is because the
existing Excel and VBA capabilities don't support cell selections from what is
known as a modeless user form. When you click in any of the five cells, a
2nd dialog box will pop up (see Figure 3). Once you have selected the
cells of interest, click the OK button in this new dialog box. It will use
your selection to enter the range into the field in the original dialog box.
You can also type in the desired information: a range address when specifying
the x or y cells, or a number when specifying the minimum x-value, maximum
x-value, and the number of data points to be used for the analysis.

Figure 3

Once all the necessary information is available, click the Update button. This will result in the
software drawing a XY Scatter chart for the x and y ranges you specified and
displaying a revised userform as shown in Figure 4. Now, the lower part of
the form becomes relevant. It contains one row for each cell that affects
the value in the plotted cell(s). If the cells are named, those names are
shown (see the references to mu, sigma, Ypdf, and Ycdf in Figure 4). The
userform also shows what the chart contains (right bottom portion in blue).
This indicates what the x-axis represents and that cells are shown on the
y-axis.

The left half of the lower portion of the form is meant for the graphical
analysis. Each row represents one cell that directly or indirectly affects
the y-axis variables. The first textbox allows you to directly enter a new
value for that variable. Alternatively, the spin buttons can be used to
increase or decrease the value. Each click of the spin button increases or
decreases the value by the multiplier amount. The default value of the
multiplier is 1 and it can be set to a smaller value (say 0.1 or 0.01) for finer
control of the analysis. As the values are changed, the impact on the
chart is shown immediately

Once done, click the Done button. All the changes made by the add-in to
the workbook will be removed.

The add-in adds a data table and a chart to the worksheet, both of which are
removed when the add-in is closed. However, it does mean that the user
-- and the add-in -- must have write access to the worksheet and the workbook.

Figure 4

Technical notes

The add-in plots the functions f(ai;x), g(aj,x) and
visually displays the effect of changes to the ais.

The add-in also demonstrates an alternative approach to implementing a
RefEdit type control in a modeless userform. Given that Microsoft has made
no improvements in the RefEdit control since...well, since whenever, this is a
functional alternative to the RefEdit control. Note that the control
doesn't work unless directly embedded in a userform displayed modal. While
not as elegant as the RefEdit, it addresses the need for a way to select an
Excel range that works in a frame, a tab strip, a page component, a COM add-in,
a userform shown modeless, or a .Net based form.

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